The objective of this project was to find a mouse strain that is susceptible to B. piliformis infection via the oral (natural) route. A susceptible strain would aid in pathogenesis studies and might act as sentinel animals to detect naturally occurring infections in rodent colonies. Mice with various immunodeficiencies were orally inoculated with B. piliformis spores. Mice were killed 5 days post-inoculation and examined for gross lesions. Tissues were also collected for histopathology. Mouse strains utilized were as follows: CBA/N, P/N, C3H/HeJ, C3H/HeN (C3H), C3H-nu, C3H-bg, C3H-xid, C3H-bg,nu; C3H-bg,xid; C3H-nu,xid. No significant gross lesions were present in any of the inoculated mice. Cecocolitis was microscopically evident in C3H-bg,nu mice, however, no B. piliformis like bacteria were observed in silver stained sections. Further studies need to be done to determine if C3H-bg,nu mice are susceptible to B. piliformis infection and, if so, if they would be a suitable sentinel animal.